Dog Whistles
http://factza.com/technology/gadgets/dog-whistles/ A dog whistle (also renowned as silent whistle or Galton's whistle) is a kind of whistle utilised in the training of dogs and cats. It was created by Francis Galton.
http://factza.com/technology/gadgets/dog-whistles/ A dog whistle (also renowned as silent whistle or Galton's whistle) is a kind of whistle utilised in the training of dogs and cats. It was created by Francis Galton.